1. Field of the Invention
The present invention relates to an offset printing apparatus provided with an ink device and a dampening fluid device. More particularly, the present invention relates to an offset printing apparatus which is a so-called keyless ink furnishing device without any means to control the quantity of ink supply for each area divided through the width of the printing plate.
2. Description of the Prior Art
A keyless ink device for an offset printing apparatus and an offset printing apparatus provided with a keyless ink device have many advantages in the process of printing as no adjustment of the ink supply in accordance with the image zone on the printing plate is necessary. Therefore, many types of such apparatuses are known. For example, Japanese Utility Model Publication No. 63-16522 entitled "Non-water ink furnishing device utilized for simplified offset printing" (hereinafter referred to as "Prior Art 1"), Japanese Patent Laid-Open Publication No. 63-57236 entitled "Ink immersing apparatus provided with no key of offset lithographic printing device" (hereinafter referred to as "Prior Art 2"), Japanese Laid-Open Publication No. 1-113244 entitled "Lithographic printing apparatus" (hereinafter referred to as "Prior Art 3") have been disclosed.
In detail, Prior Art 1 discloses an ink furnishing device comprising an ink pan having an overflow stopper which controls the reserve level of ink; a fountain roller revolving with a part immersed in the ink; a mesh roller with a doctor blade arranged between the fountain roller and a form roller in contact with the printing plate on the plate cylinder; an ink tank capable of reserving ink; a pipe with a dehydrating filter which drains the overflowed ink from the stopper; and a pipe with an ink pump, which feeds ink from the ink tank into the ink pan. In this ink furnishing device, the dampening fluid inserted into the ink pan from the printing surface is removed with the excess ink by way of passing through the dehydrating filter after overflowing from the overflow stopper, and thus the ink not affected by the dampening fluid is retained, and is resupplied to the surface of the printing plate.
Prior Art 2 discloses an ink immersing apparatus which comprises an ink pan provided with a tray having a stopper which defines the reserve level of the mixed fluid of ink and water (hereinafter referred to as "ink and others" in the explanation of the Prior Art 2) adjacent to the part reserving ink overflowed from the stopper; an ink pan provided with a device which feeds the mixture of ink and water along the full length of the tray, a pump device which connects the tray and the reserve part, and a device which can supply the new supplementary ink equivalent to the quantity consumed through printing; a pan roller which is spaced from the inner wall of the tray and which makes the ink or ink and others flow toward the stopper by revolving; a measuring roller which has a cell fixed to the pan roller and which accepts ink and others therefrom and then sends it out to the ink form roller; a scraping blade fixed to the place contacting the measuring roller at the place where the excess ink of the measuring roller is to be returned to the tray; and a measuring device of the quantity of ink for starting the device supplying the new supplementary ink for the ink pan.
As a preferred embodiment of the apparatus, the device has a constitution in which the reserve part has a capacity so that it maintains the quantity of the fluid of the ink and others to be 40% or less of the whole, a constitution in which the tray has a bow-shaped bottom which substantially matches the curve of the outer circumference surface of the pan roller, and a constitution in which the bottom of the tray is placed 6.3 mm (1/4 inch) to 25.4 mm (1 inch) apart from the surface of the pan roller. In this apparatus, the ink and others are supplied along the full length of the tray by the pump device and the ink and others are transferred to the reserve part by continuously overflowing from the stopper by the pump operation driven by the rotation of the pan roller, and the fluid in the ink can be maintained in a completely uniform quality, and thus the storage of the isolated water, which causes separation of the ink from the focused image zone of the measuring roller and the ink roller or the printing plate, can be removed.
Prior Art 3 discloses a lithography printing apparatus comprising a storage device used for storing and circulating the mixed fluid of ink and the dampening fluid (hereinafter referred to as "mixed fluid" in the explanation of Prior Art 3); an ink reservoir; a pump device, connected to the storage device and the ink reservoir, for the transfer of the mixed fluid from the storage device up to the ink reservoir; an ink supplying roller, arranged near the ink reservoir, for furnishing the mixed fluid from the ink reservoir; a metering roller, with a cell arranged to contact the ink supplying roller, for furnishing the mixed fluid from the ink supplying roller to the form roller; a scraping blade contacting the metering roller with a cell at the position where excess mixed fluid to be returned to the storage device is produced; a water sensor device connected in line with the pump device between the storage device and the ink reservoir so as to measure the quantity of water in the mixed fluid and to feedback an electric signal; a device responsive to the electric signal transmitted from the water sensor device in order to feed the predetermined quantity of the fresh ink and water as required for supplement the ink and dampening fluid consumed through the process of printing; and a device to supply the fluid, mixed with the ink and the water beforehand, to the printing plate. As a preferred embodiment of the apparatus, a device supplying mixed fluid where an ink reservoir is arranged inside of the storing device and the ink reservoir is substantially in a bow-shaped form which matches the shape of the ink supplying roller; a device supplying mixed fluid where the second scraping blade is arranged in contact with the metering roller with a cell at the position where the metering roller with a cell passes through contacting the form roller, and the storage device comprising a separate reserving hole, for storing the materials excluded from the metering roller with a cell by the second scraping blade. This separate reserving hole is connected with the pump device so as to make the operation thereof possible.
This apparatus thus supplies the quantity of ink, required for the division of ink and water to the printing plate, continuously supplementing ink to the dampening fluid consumed by adjusting the ratio of the ink and water, controlling the quantity of the ink and water by an appropriate sensor and water supplying device, in order to divide the images on the printing plate.
These prior arts have raised the following problems.
The keyless machine disclosed in Prior Art 1 is a good technology for offset printing. However, at present, it is not practical, because the quality of the dehydrating filter does not sufficiently meet the required level. The dehydrating filter thus does not last very long under continuous use, and the use of high viscosity ink is impossible.
In Prior Art 2, some improvements have been made, namely the movement of the ink on the tray in the ink pan has been improved, the capacity of the reserving portion has been enlarged, and the circulation of the ink between the reserving portion and the tray has been improved. These factors allow a more uniform dispersal of the dampening fluid inserted in the ink, thereby preventing a problem in the ink supply. Namely, in either of the rollers of the ink immersing device, especially in the pan roller, the dampening fluid is gathered partially in the ink. As a result, the surface becomes covered with a water layer and the adhesion of the ink thereto is obstructed. However, in this simple circulating operation, fractionization of the dampening fluid inserted into the ink is insufficient and therefore, prevention of the problems has not been completely realized.
Prior Art 3 discloses a device which supplies only the mixed fluid, adjusting the ink and dampening fluid to a predetermined ratio, but which does not supply ink and dampening fluid separately. It also supplies the ink and dampening fluid to the image zone and the non-image zone after separating on the surface of the printing plate or near the roller. Thus, the poor adhesion of the ink onto the roller by the water layer at the time of supplying ink and a dampening fluid, as pointed out in Prior Art 2, is avoided.
However, when the mixed fluid is supplied as described above, strict control of the mixing ratio is necessary in order to supply the quantity necessary on the surface of the printing plate. As the mixing ratio of ink and dampening fluid is continuously changeable during the printing operation due to the difference of quantity of the ink and dampening fluid consumed during ink printing and due to the return of the dampening fluid remaining in the image zone of the printing surface supplied from the supplying source through the roller, a method for completely uniformly mixing the ink and the dampening fluid and a water sensor for ink of good quality become necessary for measuring the change exactly.
Further, a method such as cooling the fluid for separating the ink from the dampening fluid is necessary in order to ensure the complete separation of the ink from the dampening fluid on the printing plate or the nearby roller.
As shown above, therefore, even in Prior Art 3, the constitution of the control parts are complicated. Thus, the possibilities of frequent breakdowns becomes higher and maintenance thereof becomes more complicated, resulting in high system cost.